Semiconductor imaging device having improved dark current performance

ABSTRACT

In some embodiments, a pixel sensor is provided. The pixel sensor includes a first photodetector arranged in a semiconductor substrate. A second photodetector is arranged in the semiconductor substrate, where a first substantially straight line axis intersects a center point of the first photodetector and a center point of the second photodetector. A floating diffusion node is arranged in the semiconductor substrate at a point that is a substantially equal distance from the first photodetector and the second photodetector. A pick-up well contact region is arranged in the semiconductor substrate, where a second substantially straight line axis that is substantially perpendicular to the first substantially straight line axis intersects a center point of the floating diffusion node and a center point of the pick-up well contact region.

REFERENCE TO RELATED APPLICATION

This Application claims priority to U.S. Provisional Application No. 62/678,871 filed on May 31, 2018, the contents of which are hereby incorporated by reference in their entirety.

BACKGROUND

Many modern day electronic devices (e.g., digital cameras, optical imaging devices, etc.) comprise image sensors. Image sensors convert optical images to digital data that may be represented as digital images. An image sensor includes an array of pixel sensors, which are unit devices for the conversion of an optical image into digital data. Some types of pixel sensors include charge-coupled device (CCD) image sensors and complementary metal-oxide-semiconductor (CMOS) image sensors. Compared to CCD pixel sensors, CMOS pixel sensors are favored due to low power consumption, small size, fast data processing, a direct output of data, and low manufacturing cost.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 illustrates a layout view of some embodiments of a pixel sensor having a pick-up well contact region and floating diffusion node positioned to reduce dark current and dark current imbalances.

FIGS. 2A-2C illustrate various views of an integrated chip (IC) comprising the pixel sensor of FIG. 1.

FIG. 3 illustrates some embodiments of an image sensor 300 having a plurality of integrated chips (ICs) each represented by the IC of FIGS. 2A-2C.

FIGS. 4A-4C through 10A-10C illustrate a series of various views of some embodiments of a method for forming the integrated chip (IC) of FIGS. 2A-2C.

FIG. 11 illustrates a flowchart of some embodiments of a method for forming the integrated chip (IC) of FIGS. 2A-2C.

DETAILED DESCRIPTION

The present disclosure will now be described with reference to the drawings wherein like reference numerals are used to refer to like elements throughout, and wherein the illustrated structures are not necessarily drawn to scale. It will be appreciated that this detailed description and the corresponding figures do not limit the scope of the present disclosure in any way, and that the detailed description and figures merely provide a few examples to illustrate some ways in which the inventive concepts can manifest themselves.

The present disclosure provides many different embodiments, or examples, for implementing different features of this disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Some complementary metal-oxide semiconductor image sensors (CISs) have an array of pixel sensors. A pixel sensor records incident radiation using a photodetector, and facilitates digital readout of the recording with a plurality of pixel devices (e.g., a transfer transistor, a reset transistor, a source follower transistor, and/or a row-select transistor). Some pixel sensors comprise an array of photodetectors (e.g., a 2×2 photodetector pixel sensor). In such pixel sensors, a plurality of photodetector collector regions are disposed in a pixel sensor well region. Further, the photodetectors share a common floating diffusion node (e.g., a region of the semiconductor substrate in which the photodetectors may respectively transfer accumulated charge during readout), common pixel devices (e.g., a reset transistor, a source follower transistor, and/or a row-select transistor), and a pick-up well contact region. The pick-up well contact region provides a region of low resistance between a conductive contact and the pixel sensor well region. During operation, a bias voltage is applied to the pixel sensor well region via the conductive contact, such that the photodetectors are reverse-biased.

One challenge with the above pixel sensors is dark current. Dark current is electrical current that passes through the photodetectors even when no photons are entering the photodetector. One dark current source is due to the location (and/or proximity) of the pick-up well contact region in relation to the photodetectors and the floating diffusion node. For example, in a 2×2 photodetector pixel sensor, one of the photodetectors is typically disposed directly between the floating diffusion node and the pick-up well contact region, such that a substantially straight line axis that intersects a center point of the floating diffusion node and the pick-up well contact region also intersects the collector region of the one of the photodetectors. Because the photodetector is arranged between the floating diffusion node and the pick-up well contact region, dark current from the pick-up well contact region increases within the photodetector, thereby causing the photodetector to suffer from poor dark current performance. Furthermore, in such a layout the pick-up well contact region is arranged at different distances from the photodetectors. The different distances cause the dark current from the pick-up well contact region to affect the different photodetectors differently, resulting in large dark current imbalances between the different photodetectors (e.g., differences in dark current between the individual photodetectors of the sensor).

The present application is directed toward a pixel sensor having a plurality of photodetectors. The pixel sensor has a pick-up well contact region that is arranged at a position that is a substantially equal distance from the plurality of photodetectors and that is separated from a floating diffusion node by a path extending between adjacent ones of the plurality of photodetectors. By having the pick-up well contact region arranged at a substantially equal distance from the plurality of photodetectors, large dark current imbalances can be reduced. Furthermore, because the pick-up well contact region is separated from a floating diffusion node by a path extending between adjacent ones of the plurality of photodetectors, the floating diffusion node can drain the dark current generated by the pick-up well contact region before the dark current interacts with the plurality of photodiodes. Accordingly, the pixel sensor of the present disclosure may have improved dark current performance.

In various embodiments, the pixel sensor may have a first photodetector and a second photodetector disposed in a semiconductor substrate, where a first substantially straight line axis intersects a center point of the first photodetector and a center point of the second photodetector. A floating diffusion node is disposed in the semiconductor substrate between the first photodetector and the second photodetector. Further, a pick-up well contact region is disposed in the semiconductor substrate, where a second substantially straight line axis that is substantially perpendicular to the first substantially straight line axis intersects a center point of the floating diffusion node and a center point of the pick-up well contact region. Because the floating diffusion node is disposed between the first photodetector and the second photodetector and because the second substantially straight line axis is substantially perpendicular to the first substantially straight line axis, the pick-up well contact region is spaced about equidistant from the first photodetector and the second photodetector, thereby reducing dark current imbalances in the pixel sensor. Further, because the center points of the pick-up well contact region and the floating diffusion node are arranged along a substantially straight line axis that is between the first photodetector and the second photodetector, the floating diffusion node may drain more of the dark current generated by the pick-up well contact region, thereby preventing the dark current from interacting with the photodetectors and reducing overall dark current of the pixel sensor. Put differently, as the substantially straight line axis between center points of the pick-up well contact region and the floating diffusion node does not extend across the first and second photodetectors, dark current between the pick-up well contact region and the floating diffusion node is less likely to interact with the first and second photodetectors. For example, the dark current may be reduced by between approximately 20% and approximately 50% (e.g., from approximately 4.2 electrons/pixel/second (e/p/s) to approximately 3.0 e/p/s).

FIG. 1 illustrates a layout view of some embodiments of a pixel sensor 100 having a pick-up well contact region and floating diffusion node positioned to reduce dark current and dark current imbalances.

As shown in FIG. 1, the pixel sensor 100 comprises a pixel sensor well region 102 disposed in a semiconductor substrate 104. In some embodiments, the semiconductor substrate 104 comprises any type of semiconductor body (e.g., monocrystalline silicon/CMOS bulk, silicon-germanium (SiGe), silicon on insulator (SOI), etc.). The pixel sensor well region 102 is a region of the semiconductor substrate 104 having a first doping type (e.g., p-type doping).

A plurality of photodetectors 106 a-d are disposed in the semiconductor substrate 104. In some embodiments, the photodetectors 106 a-d are arranged in an array comprising a plurality of rows (e.g., along an x-axis) and columns (e.g., along a y-axis). The photodetectors 106 a-d are configured to absorb incident radiation (e.g., photons) and generate respective electrical signals corresponding to the incident radiation. In some embodiments, each of the photodetectors 106 a-d comprise a photodetector collector region 108 disposed in the pixel sensor well region 102. In further embodiments, the photodetector collector regions 108 are discrete regions of the semiconductor substrate 104 having a second doping type (e.g., n-type doping) opposite the first doping type. In yet further embodiments, the photodetectors 106 a-d each comprise a photodetector collector region 108 and portions of the pixel sensor well region 102 disposed around the photodetector collector region 108 in which a depletion region has formed (e.g., due to p-n junctions between the photodetector collector regions 108 and the pixel sensor well region 102).

In some embodiments, the plurality of photodetectors 106 a-d comprise a first photodetector 106 a, a second photodetector 106 b, a third photodetector 106 c, and a fourth photodetector 106 d. In some embodiments, a first substantially straight line axis 110 extends in a first direction (e.g., along the x-axis) and intersects a center point of the first photodetector 106 a and a center point of the second photodetector 106 b. In further embodiments, a second substantially straight line axis 112 that is parallel to the first substantially straight line axis 110 intersects a center point of the third photodetector 106 c and a center point of the fourth photodetector 106 d. In further embodiments, a third substantially straight line axis 114 extends in a second direction (e.g., along the y-axis) substantially perpendicular to the first direction and intersects the center point of the first photodetector 106 a and the center point of the third photodetector 106 c. In yet further embodiments, a fourth substantially straight line axis 116 that is parallel to the third substantially straight line axis 114 intersects the center point of the second photodetector 106 b and a center point of the fourth photodetector 106 d.

A floating diffusion node 118 is disposed in the pixel sensor well region 102. The floating diffusion node 118 is a region of the semiconductor substrate 104 having the second doping type (e.g., n-type doping). In some embodiments, the floating diffusion node 118 is disposed between the first photodetector 106 a, second photodetector 106 b, third photodetector 106 c, and fourth photodetector 106 d. In some embodiments, the floating diffusion node 118 is disposed at a substantially equal distance from the first photodetector 106 a, second photodetector 106 b, third photodetector 106 c, and fourth photodetector 106 d. In further embodiments, the center point of the floating diffusion node is spaced about a same distance from the first substantially straight line axis 110 as the second substantially straight line axis 112. In further embodiments, the center point of the floating diffusion node is spaced about a same distance from the third substantially straight line axis 114 as the fourth substantially straight line axis 116. In yet further embodiments, a center point of the floating diffusion node 118 is spaced about equidistant from the center points of the photodetectors 106 a-d.

A pick-up well contact region 120 is disposed in the pixel sensor well region 102. The pick-up well contact region 120 is configured to provide a low resistance region between the pixel sensor well region 102 and a conductive contact (not shown). The pick-up well contact region 120 is a region of the semiconductor substrate 104 having the first doping type (e.g., p-type doping). In some embodiments, the pick-up well contact region 120 has a higher concentration of the first doping type than the pixel sensor well region 102.

A fifth substantially straight line axis 122 extends in the second direction and intersects the center point of the floating diffusion node 118 and a center point of the pick-up well contact region 120. In some embodiments, the floating diffusion node 118 is disposed on a first side of the second substantially straight line axis 112 between the third substantially straight line axis 114 and the fourth substantially straight line axis 116. In further embodiments, the pick-up well contact region 120 is disposed between the third substantially straight line axis 114 and the fourth substantially straight line axis 116 on a second side of the second substantially straight line axis 112 opposite the first side. In yet further embodiments, the fifth substantially straight line axis 122 extends in the second direction between the photodetector collector region 108 of the first photodetector 106 a and the photodetector collector region 108 of the second photodetector 106 b.

In some embodiments, the fifth substantially straight line axis 122 is substantially perpendicular to the first substantially straight line axis 110 and/or the second substantially straight line axis 112. In further embodiments, the fifth substantially straight line axis 122 is substantially parallel to the third substantially straight line axis 114 and/or the fourth substantially straight line axis 116. In further embodiments, the fifth substantially straight line axis 122 intersects the first substantially straight line axis 110 at a mid-point between the center point of the first photodetector 106 a and the center point of the second photodetector 106 b. In further, the fifth substantially straight line axis 122 intersects the second substantially straight line axis 112 at a mid-point between the center point of the third photodetector 106 c and the center point of the fourth photodetector 106 d. In yet further embodiments, the center point of the pick-up well contact region 120 is spaced about equidistant from the center point of the third photodetector 106 c and the center point of the fourth photodetector 106 d.

Because the pick-up well contact region 120 is spaced about equidistant from the third photodetector 106 c and the fourth photodetector 106 d, dark current imbalances between the third photodetector 106 c and the fourth photodetector 106 d may be reduced. Further, because the fifth substantially straight line axis 122 extends in the second direction between the photodetector collector region 108 of the third photodetector 106 c and the photodetector collector region 108 of the fourth photodetector 106 d, the floating diffusion node 118 may drain more of the dark current generated by the pick-up well contact region 120. Because the floating diffusion node 118 may drain more of the dark current generated by the pick-up well contact region 120, overall dark current of the pixel sensor 100 may be reduced. That is, because the fifth substantially straight line axis 122 does not cross into the photodetector collector regions 108 of the third and fourth photodetectors 106 c and 106 d, the third and fourth photodetectors 106 c and 106 d are not in the path along which the dark current passes. Accordingly, dark current performance of the pixel sensor 100 may be improved.

FIGS. 2A-2C illustrates various views of an integrated chip (IC) 200 comprising the pixel sensor 100 of FIG. 1. FIG. 2A illustrates a view of the IC 200 facing a front-side 104 f of a semiconductor substrate 104. FIG. 2B illustrates a cross-sectional view taken along line A-A′ of FIG. 2A. FIG. 2C illustrates a cross-sectional view taken along line B-B′ of FIG. 2A.

As shown in FIGS. 2A-2C, a plurality of transfer transistors 224 are disposed on a front-side 104 f of the semiconductor substrate 104. In some embodiments, the transfer transistors 224 are respectively disposed between the floating diffusion node 118 and the center points of the photodetectors 106 a-d. The transfer transistors 224 may selectively form a conductive channel between the photodetectors 106 a-d and the floating diffusion node 118 to transfer accumulated charge (e.g., via absorbing incident radiation) in the photodetectors 106 a-d to the floating diffusion node 118.

In some embodiments, the transfer transistors 224 each comprise a transfer transistor gate electrode 226 disposed on a transfer transistor gate dielectric 228, such that the transfer transistor gate dielectric 228 separates the transfer transistor gate electrode 226 from the front-side 104 f of the semiconductor substrate 104. In some embodiments, the transfer transistor gate electrodes 226 and the transfer transistor gate dielectrics 228 may have a triangular layout when viewing the front-side 104 f of the semiconductor substrate 104.

In some embodiments, the transfer transistor gate electrodes 226 may comprise, for example, doped polysilicon, fully-silicided polysilicon, a metal (e.g., aluminum), or the like. In further embodiments, the transfer transistor gate dielectrics 228 may comprise, for example, an oxide (e.g., SiO₂), a nitride (e.g., silicon nitride), a high-k dielectric (e.g., hafnium oxide), or the like. In further embodiments, transfer transistor sidewall spacers 230 are disposed along sidewalls of the transfer transistor gate electrodes 226 and the transfer transistor gate dielectrics 228. In yet further embodiments, the transfer transistor sidewall spacers 230 may comprise, for example, an oxide, a nitride, a carbide, or the like.

Also shown in FIGS. 2A-2C, the IC 200 comprises a pixel device region 232. In some embodiments, the pixel device region 232 comprises a reset transistor 234, a source follower transistor 236, and/or a row-select transistor 238. In further embodiments, the reset transistor 234, the source follower transistor 236, and the row-select transistor 238 each comprise a pixel device gate electrode 240 stacked on a pixel device gate dielectric 242. In further embodiments, the pixel device gate electrodes 240 may comprise, for example, doped polysilicon, fully-silicided polysilicon, a metal (e.g., aluminum), or the like. In yet further embodiments, the pixel device gate dielectrics 242 may comprise, for example, an oxide, a nitride, a high-k dielectric, or the like.

The reset transistor 234, the source follower transistor 236, and the row-select transistor 238 each comprise source/drain regions 244 disposed on opposite sides of respective pixel device gate electrodes 240. In some embodiments, the source/drain regions 244 are regions of the semiconductor substrate 104 having the second doping type (e.g., n-type doping). In further embodiments, one of the source/drain regions 244 is a common source/drain region 244 shared by the reset transistor 234 and the source follower transistor 236. In further embodiments, another one of the source/drain regions 244 is a common source/drain region 244 shared by the row-select transistor 238 and the source follower transistor 236. In further embodiments, pixel device sidewall spacers 246 are respectively disposed along sidewalls of the pixel device gate electrodes 240 and the pixel device gate dielectrics 242. In yet further embodiments, the pixel device sidewall spacers 246 may comprise, for example, an oxide, a nitride, a carbide, or the like.

A pixel device region isolation structure 248 is disposed in the semiconductor substrate 104 and around sides of the reset transistor 234, the source follower transistor 236, and the row-select transistor 238. The pixel device region isolation structure 248 is configured to provide electrical isolation between the photodetectors 106 a-d and the pixel device region 232. In some embodiments, the pixel device region isolation structure 248 may contact the source/drain regions 244 of the reset transistor 234, the source follower transistor 236, and the row-select transistor 238. In other embodiments, the pixel device region isolation structure 248 may be separated by non-zero distances from the source/drain regions 244 of the reset transistor 234, the source follower transistor 236, and the row-select transistor 238. In further embodiments, the pixel device region isolation structure 248 may be, for example, a shallow trench isolation (STI) structure, a deep trench isolation (DTI) structure, or the like. In other embodiments, the pixel device region isolation structure 248 may be an isolation well comprising regions of the semiconductor substrate 104 having the first doping type (e.g., p-type doping). In such an embodiment, an isolation voltage may be applied to the isolation well to provide electrical isolation between the photodetectors 106 a-d and the pixel device region 232.

In some embodiments, the pixel device gate electrodes 240, the pixel device gate dielectrics 242, and/or the pixel device sidewall spacers 246 may extend in the second direction (e.g., along the y-axis) beyond inner sidewalls of the pixel device region isolation structure 248. In further embodiments, outer sidewalls of the pixel device region isolation structure 248 define outer sides of the pixel device region 232. In further embodiments, the pick-up well contact region 120 is disposed outside of the pixel device region 232. In yet further embodiments, the pick-up well contact region 120 contacts the pixel device region isolation structure 248. In other embodiments, the pick-up well contact region 120 may be separated from the pixel device isolation structure 248 by a non-zero distance.

In some embodiments, a sixth substantially straight line axis 250 extends in the first direction and intersects the center point of the pick-up well contact region 120, center points of the source/drain regions 244, and center points of the pixel device gate electrodes 240. The sixth substantially straight line axis 250 may be substantially perpendicular to the fifth substantially straight line axis 122 and substantially parallel to the first substantially straight line axis 110. In some embodiments, the pixel device region isolation structure 248 may extend in the first direction along the sixth substantially straight line axis 250, such that outer sidewalls of the pixel device region isolation structure 248 that extend in the first direction are substantially parallel to the sixth substantially straight line axis 250.

An interconnect structure 252 comprising an interlayer dielectric (ILD) layer 254 and a plurality of conductive contacts 256 is disposed on the front-side 104 f of the semiconductor substrate 104. The ILD layer 254 is disposed on front-side 104 f of the semiconductor substrate 104 and may contact the pixel sensor well region 102, the floating diffusion node 118, the transfer transistors 224, the pick-up well contact region 120, the pixel device region isolation structure 248, the reset transistor 234, the source follower transistor 236, and the row-select transistor 238. In further embodiments, the ILD layer 254 may comprise one or more of a low-k dielectric layer (e.g., a dielectric with a dielectric constant less than about 3.9), an ultra-low-k dielectric layer, or an oxide (e.g., silicon oxide). Further, the conductive contacts 256 are disposed in the ILD layer 254. In further embodiments, the conductive contacts 256 may comprise, for example, tungsten, copper, or the like.

In some embodiments, the conductive contacts 256 extend through the ILD layer 254 to contact the transfer transistor gate electrodes 226, the floating diffusion node 118, the pick-up well contact region 120, the source/drain regions 244, and the pixel device gate electrodes 240. In further embodiments, a conductive contact 256 may not extend through the ILD layer 254 to contact the common source/drain region 244 shared by the source follower transistor 236 and the row-select transistor 238. In further embodiments, the sixth substantially straight line axis 250 intersects the conductive contacts 256 that contact the pick-up well contact region 120, the source/drain regions 244, and the pixel device gate electrodes 240. In further embodiments, the fifth substantially straight line axis 122 intersects the conductive contacts 256 that contact the pick-up well contact region 120 and the floating diffusion node 118.

In some embodiments, a plurality of back-side isolation (BSI) structures 258 are disposed in the semiconductor substrate 104. The BSI structures 258 extend into the semiconductor substrate 104 from a back-side 104 b of the semiconductor substrate 104. The BSI structures 258 may be respectively disposed between the photodetectors 106 a-d. In some embodiments, one of the BSI structures 258 may extend in the second direction over both the floating diffusion node 118 and the pick-up well contact region 120. In further embodiments, the BSI structures 258 may be back-side deep trench isolation structures.

In some embodiments, an anti-reflection layer 260 is disposed on the back-side 104 b of the semiconductor substrate 104. In some embodiments, the anti-reflection layer 260 contacts the pixel sensor well region 102 and the BSI structures 258. The anti-reflection layer 260 is configured to reduce the amount of incident radiation reflected by the semiconductor substrate 104. In some embodiments, the anti-reflection layer 260 comprises, for example, an oxide, a high-k dielectric, a nitride, or the like. In further embodiments, the anti-reflection layer 260 may comprise a first layer comprising an oxide stacked on a second layer comprising a high-k dielectric, or vice versa.

A plurality of color filters 262 (e.g., a red color filer, a blue color filter, a green color filer, etc.) are disposed on the anti-reflection layer 260. In some embodiments, the color filters 262 are arranged in an array over the anti-reflection layer 260. In such an embodiment, the color filters 262 are respectively disposed over the photodetectors 106 a-d. The color filters 262 are respectively configured to transmit specific wavelengths of incident radiation. For example, a first color filter (e.g., the red color filter) may transmit light having wavelengths within a first range, while a second color filter (e.g., the blue color filter) may transmit light having wavelengths within a second range different than the first range. Further, a plurality of micro-lenses 264 are disposed on the color filters 262. In some embodiments, the micro-lenses 264 are respectively disposed over the color filters 262. The micro-lenses 264 are configured to focus incident radiation (e.g., photons) towards the photodetectors 106 a-d.

FIG. 3 illustrates some embodiments of an image sensor 300 having a plurality of integrated chips (ICs) each represented by the IC 200 of FIGS. 2A-2C.

As shown in FIG. 3, the ICs 200 are arranged in an array comprising a plurality of rows of ICs (e.g., along an x-axis) and a plurality of columns of ICs (e.g., along a y-axis). In some embodiments, the ICs 200 respectively comprise conductive lines 302. The conductive lines 302 electrically couple together the floating diffusion node 118 of each IC 200, one of the source/drain regions 244 of the reset transistor 234 of each IC 200, and the pixel device gate electrode 240 of the source follower transistor 236 of each IC 200.

In some embodiments, the conductive lines 302 are disposed in the interconnect structure 252 (e.g., as shown in the cross-sectional view of FIG. 2C). In such an embodiment, the conductive lines 302 may be disposed in an inter-metal dielectric (IMD) layer (not shown in FIG. 2C) disposed on the ILD layer 254 and the conductive contacts 256, so that the conductive lines 302 and the IMD layer are vertically separated from the front-side 104 f of the semiconductor substrate 104 by the ILD layer 254. In some embodiments, the conductive lines 302 may comprise, for example, copper, aluminum, or the like. In further embodiments, the IMD layer may comprise, for example, a low-k dielectric layer, an ultra-low-k dielectric layer, an oxide, or the like. In yet further embodiments, the pixel device region 232 of some of the ICs 200 may extend along the first direction (e.g., along the x-axis) between a third photodetector 106 c of a first IC 200 disposed in an adjacent column of ICs and between a first photodetector 106 a of a second IC 200 disposed in the adjacent column of ICs, where the first IC 200 and the second IC 200 are arranged in adjacent rows of ICs.

FIG. 4A-4C through 10A-10C illustrate a series of various views of some embodiments of a method for forming the integrated chip (IC) of FIGS. 2A-2C. Figures with a suffix of “A” illustrate either a front-side facing view of the IC or a back-side facing view of the IC that correspond to an orientation of the IC during various formation processes. Figures with a suffix of “B” are taken along line A-A′ of Figs. with a suffix of “A.” Figures with a suffix of “C” are taken along line B-B′ of Figs. with a suffix of “A.”

As shown in FIGS. 4A-4C, a pixel device region isolation structure 248 is formed in the semiconductor substrate 104. In some embodiments, the pixel device region isolation structure 248 may be formed by selectively etching the semiconductor substrate 104 to form a trench in the semiconductor substrate 104 that extends into the semiconductor substrate 104 from a front-side 104 f of the semiconductor substrate 104, and subsequently filling (e.g., by chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), thermal oxidation, sputtering, etc.) the trench with a dielectric material. In further embodiments, the semiconductor substrate 104 is selectively etched by forming a masking layer (not shown) on the front-side 104 f of the semiconductor substrate 104, and subsequently exposing the semiconductor substrate 104 to an etchant configured to selectively remove unmasked portions of the semiconductor substrate 104. In yet further embodiments, the dielectric material may comprise an oxide (e.g., silicon oxide), a nitride, or the like. In other embodiments, the pixel device region isolation structure 248 may be an isolation well. In such an embodiment, the isolation well may be formed by a selective ion implantation process that utilizes a masking layer (not shown) on the front-side 104 f of the semiconductor substrate 104 to selectively implant ions into the semiconductor substrate 104.

As shown in FIGS. 5A-5C, a pixel sensor well region 102 is formed in the semiconductor substrate 104. The pixel sensor well region 102 is a region of the semiconductor substrate 104 having a first doping type (e.g., p-type doping). In some embodiments, the pixel sensor well region 102 may be formed by a selective ion implantation process that utilizes a masking layer (not shown) on the front-side 104 f of the semiconductor substrate 104 to selectively implant ions into the semiconductor substrate 104. In other embodiments, the pixel sensor well region 102 may be formed by a blanket ion implantation process (e.g., an unmasked ion implantation) to implant ions into the semiconductor substrate 104.

Also shown in FIGS. 5A-5C, a plurality of photodetectors 106 a-d are formed in the semiconductor substrate 104. The photodetectors 106 a-d each comprise a photodetector collector region 108 and portions of the pixel sensor well region 102 disposed around the photodetector collector region 108 in which a depletion region has formed (e.g., due to p-n junctions between the photodetector collector regions 108 and the pixel sensor well region 102). In some embodiments, the plurality of photodetectors 106 a-d comprise a first photodetector 106 a, a second photodetector 106 b, a third photodetector 106 c, and a fourth photodetector 106 d.

In some embodiments, a process for forming the photodetectors 106 a-d comprises forming a plurality of photodetector collector regions 108 in the pixel sensor well region 102. The photodetector collector regions 108 are discrete regions of the semiconductor substrate 104 having a second doping type (e.g., n-type doping) opposite the first doping type. In some embodiments, the photodetector collector regions 108 may be formed by a selective ion implantation process that utilizes a masking layer (not shown) on the front-side 104 f of the semiconductor substrate 104 to selectively implant ions into the semiconductor substrate 104. Because the photodetector collector regions 108 and the pixel sensor well region 102 have opposite doping types, depletion regions (shown as a region surrounded by dotted lines) form in portions of the pixel sensor well region 102 disposed around each photodetector collector region 108.

As shown in FIGS. 6A-6C, transfer transistor gate dielectrics 228 are formed on the front-side 104 f of the semiconductor substrate 104, and transfer transistor gate electrodes 226 are respectively formed on the transfer transistor gate dielectrics 228. Further, pixel device gate dielectrics 242 are formed on the front-side 104 f of the semiconductor substrate 104, and pixel device gate electrodes 240 are respectively formed on the pixel device gate dielectrics 242. In some embodiments, when viewing the front-side 104 f of the semiconductor substrate 104, the transfer transistor gate dielectrics 228 and the transfer transistor gate electrodes 226 may be formed with a triangular layout.

In some embodiments, a process for forming the transfer transistor gate dielectrics 228, the pixel device gate dielectrics 242, the transfer transistor gate electrodes 226, and the pixel device gate electrodes 240 comprises depositing and/or growing (e.g., by CVD, PVD, ALD, thermal oxidation, sputtering, etc.) a gate dielectric layer on the front-side 104 f of the semiconductor substrate 104. Next, a gate electrode layer may be deposited (e.g., by CVD, PVD, ALD, sputtering, electrochemical plating, electroless plating, etc.) on the gate dielectric layer. Subsequently, the gate dielectric layer and the gate electrode layer are patterned and etched to form the transfer transistor gate dielectrics 228, the pixel device gate dielectrics 242, the transfer transistor gate electrodes 226, and the pixel device gate electrodes 240. In further embodiments, the gate electrode layer may comprise, for example, polysilicon, aluminum, or the like. In yet further embodiments, the gate dielectric layer may comprise, for example, an oxide, a high-k dielectric, or the like.

Also shown in FIGS. 6A-6C, transfer transistor sidewall spacers 230 are formed on the front-side 104 f of the semiconductor substrate 104 and along sidewalls of the transfer transistor gate electrodes 226 and sidewalls of the transfer transistor gate dielectrics 228. Further, pixel device sidewall spacers 246 are formed on the front-side 104 f of the semiconductor substrate 104 and along sidewalls of the pixel device gate electrodes 240 and sidewalls of the pixel device gate dielectrics 242.

In some embodiments, the transfer transistor sidewall spacers 230 and the pixel device sidewall spacers 246 may be formed by depositing (e.g., by CVD, PVD, ALD, sputtering, etc.) a spacer layer over the front-side 104 f of the semiconductor substrate 104, the transfer transistor gate dielectrics 228, the pixel device gate dielectrics 242, the transfer transistor gate electrodes 226, and the pixel device gate electrodes 240. In further embodiments, the spacer layer is subsequently etched to remove the spacer layer from horizontal surfaces, thereby forming the transfer transistor sidewall spacers 230 along sidewalls of the transfer transistor gate electrodes 226 and sidewalls of the transfer transistor gate dielectrics 228 and forming the pixel device sidewall spacers 246 along sidewalls of the pixel device gate electrodes 240 and sidewalls of the pixel device gate dielectrics 242. In further embodiments, the spacer layer may comprise a nitride, an oxide, or some other dielectric. In yet further embodiments, before the transfer transistor sidewall spacers 230 and the pixel device sidewall spacers 246 are formed, lightly-doped source/drain extensions (not shown) may be formed in the semiconductor substrate 104 on opposing sides of the pixel device gate electrodes 240. In such an embodiment, the lightly-doped source/drain extensions (not shown) may be formed by a selective ion implantation process that utilizes a masking layer (not shown) on the front-side 104 f of the semiconductor substrate 104 to selectively implant ions into the semiconductor substrate 104.

As shown in FIGS. 7A-7C, source/drain regions 244 are formed in the semiconductor substrate 104 on opposing sides of the pixel device gate electrodes 240. In some embodiments, the source/drain regions 244 are regions of the semiconductor substrate 104 having the second doping type (e.g., n-type doping). In further embodiments, sides of some of the source/drain regions 244 are substantially aligned with opposing outer sidewalls of the pixel device sidewall spacers 246. In yet further embodiments, the source/drain regions 244 may contact respective lightly-doped source/drain extensions (not shown). In such an embodiment, the lightly-doped source/drain extensions may have a lower concentration of the second doping type than the source/drain regions. In further such embodiments, the sides of the lightly-doped source/drain extensions facing the pixel device gate electrodes 240 may align with sidewalls of the pixel device gate electrodes 240 and/or the pixel device gate dielectrics 242. In some embodiments, the source/drain regions 244 may be formed by a first selective ion implantation process that utilizes a masking layer (not shown) disposed on the front-side 104 f of the semiconductor substrate 104 to selectively implant n-type dopants (e.g., phosphorus) into the semiconductor substrate 104.

In some embodiments, a reset transistor 234, a source follower transistor 236, and a row-select transistor 238 each comprise a pixel device gate electrode 240 stacked on a pixel device gate dielectric 242. Further, the reset transistor 234, the source follower transistor 236, and the row-select transistor 238 each comprise source/drain regions 244 respectively disposed on opposite sides of the pixel device gate electrode 240 and the pixel device gate dielectric 242 stacks. In further embodiments, the reset transistor 234, the source follower transistor 236, and the row-select transistor 238 may be disposed in a pixel device region 232. In such an embodiment, outer sides of the pixel device region isolation structure 248 may define outer sides of the pixel device region 232.

Also shown in FIG. 7A-7C, a pick-up well contact region 120 is formed in the pixel sensor well region 102. The pick-up well contact region 120 is a region of the semiconductor substrate 104 having the first doping type (e.g., p-type doping). In some embodiments, the pick-up well contact region 120 has a higher concentration of the first doping type than the pixel sensor well region 102. In some embodiments, the pick-up well contact region 120 is formed outside the pixel device region 232. In further embodiments, the pick-up well contact region 120 may be formed contacting the pixel device region isolation structure 248. In yet further embodiments, the pick-up well contact region 120 is formed in a first substantially straight line with the pixel device region 232, such that the first substantially straight line axis that extends in a first direction intersects a center point of the pick-up well contact region 120, center points of the source/drain regions 244, center points of the pixel device gate electrodes 240, and center points of the pixel device gate dielectrics 242.

In some embodiments, the pick-up well contact region 120 may be formed by a second selective ion implantation process that utilizes a masking layer (not shown) on the front-side 104 f of the semiconductor substrate 104 to selectively implant p-type dopants (e.g., boron) into the semiconductor substrate 104. In further embodiments, the second selective ion implantation process may be performed before the first selective ion implantation process. In other embodiments, the first selective ion implantation process may be performed before the second selective ion implantation process.

Also shown in FIG. 7A-7C, a floating diffusion node 118 is formed in the pixel sensor well region 102 between the photodetectors 106 a-d. The floating diffusion node 118 is a region of the semiconductor substrate having the second doping type (e.g., n-type doping). In some embodiments, the floating diffusion node 118 is formed in a second substantially straight line with the pick-up well contact region 120, such that the second substantially straight line axis that extends in a second direction substantially perpendicular to the first direction intersects a center point of the pick-up well contact region 120 and a center point of the floating diffusion node 118. In further embodiments, the second substantially straight line axis may be substantially perpendicular to a third substantially straight line axis that intersects a center point of the first photodetector 106 a and a center point of the second photodetector 106 b. In yet further embodiments, the second substantially straight line axis may be substantially perpendicular to a fourth substantially straight line axis that intersects a center point of the third photodetector 106 c and a center point of the fourth photodetector 106 d.

In some embodiments, the floating diffusion node 118 may be formed by the first ion implantation process. In such an embodiment, the floating diffusion node 118 and the source/drain regions 244 may have about the same concentration of the second doping type. In other embodiments, the floating diffusion node 118 may be formed by a third selective ion implantation process that utilizes a masking layer (not shown) on the front-side 104 f of the semiconductor substrate 104 to selectively implant n-type dopants (e.g., phosphorus) into the semiconductor substrate 104. In such an embodiment, the third selective ion implantation process may be performed before the first selective ion implantation process, or vice versa, or before the second selective ion implantation process, or vice versa. In further embodiments, an anneal process (e.g., laser anneal, rapid thermal anneal (RTA), etc.) is performed, after the source/drain regions 244, the pick-up well contact region 120, and the floating diffusion node 118 are formed, to activate the dopants.

As shown in FIGS. 8A-8C, an interlayer dielectric (ILD) layer 254 is formed on the front-side 104 f of the semiconductor substrate 104. In some embodiments, the ILD layer 254 is formed on the pixel sensor well region 102, the source/drain regions 244, the pixel device region isolation structure 248, the pick-up well contact region 120, the floating diffusion node 118, the pixel device gate electrodes 240, the transfer transistor gate electrodes 226, the pixel device sidewall spacers 246, and the transfer transistor sidewall spacers 230. The ILD layer 254 may be formed with a substantially planar upper surface and may comprise an oxide, a nitride, a low-k dielectric, or the like. In some embodiments, the ILD layer 254 may be formed by CVD, PVD, ALD, sputtering, or the like. In further embodiments, a planarization process (e.g., a chemical-mechanical planarization (CMP)) may be performed on the ILD layer 254 to form the substantially planar upper surface.

Also shown in FIGS. 8A-8C, a plurality of conductive contacts 256 are formed in the ILD layer 254 that respectively extend through the ILD layer 254 to the transfer transistor gate electrodes 226, the floating diffusion node 118, the pick-up well contact region 120, the source/drain regions 244, and the pixel device gate electrodes 240. In some embodiments, a conductive contact 256 may not be formed in the ILD layer 254 that extends through the ILD layer 254 to the source/drain region 244 disposed between the pixel device gate electrode 240 of the source follower transistor 236 and the pixel device gate electrode 240 of the row-select transistor 238. In further embodiments, a process for forming the conductive contacts 256 comprises performing an etch into the ILD layer 254 to form contact openings that correspond to the conductive contacts 256. In further embodiments, the etch may be performed with a patterned masking layer formed over the ILD layer 254. In yet further embodiments, the contact openings may be filled by depositing or growing a conductive material (e.g., tungsten) covering the ILD layer 254 that fills the contact openings, and subsequently performing a planarization process (e.g., CMP) on the conductive contacts 256 and ILD layer 254.

As shown in FIGS. 9A-9C, in some embodiments, the semiconductor substrate 104 is thinned, such that the semiconductor substrate 104 has a reduced thickness. In further embodiments, the thinning may expose the pixel sensor well region 102 on the back-side 104 b of the semiconductor substrate 104. The thinning may be, for example, performed by a planarization process, an etch back process, or the like. In further embodiments, the planarization process may be a CMP process.

Also shown in FIGS. 9A-9C, a plurality of back-side isolation (BSI) structures 258 are formed in the semiconductor substrate 104. The BSI structures 258 extend into the semiconductor substrate 104 from a back-side 104 b of the semiconductor substrate 104 opposite the front-side 104 f. In some embodiments, the BSI structures 258 are formed in the semiconductor substrate 104 around sides of each of the photodetector collector regions 108.

In some embodiments, a process for forming the BSI structures 258 comprises selectively etching the semiconductor substrate 104 to form trenches in the semiconductor substrate 104 that extend into the semiconductor substrate 104 from the back-side 104 b of the semiconductor substrate 104, and subsequently filling the trenches (e.g., by CVD, PVD, ALD, thermal oxidation, sputtering, etc.) with a dielectric material. In further embodiments, the semiconductor substrate 104 is selectively etched by forming a masking layer (not shown) on the back-side 104 b of the semiconductor substrate 104, and subsequently exposing the semiconductor substrate 104 to an etchant configured to selectively remove unmasked portions of the semiconductor substrate 104. In further embodiments, the dielectric material may comprise an oxide, a nitride, or the like. In yet further embodiments, a planarization process (e.g., CMP) may be performed on the dielectric layer and the back-side 104 b of the semiconductor substrate 104 to form a substantially planar surface.

As shown in FIGS. 10A-10C, an anti-reflection layer 260 is formed on the back-side 104 b of the semiconductor substrate 104. In some embodiments, the anti-reflection layer 260 is formed on the pixel sensor well region 102 and the BSI structures 258. The anti-reflection layer 260 is configured to reduce the amount of incident radiation reflected by the semiconductor substrate 104. In some embodiments, the anti-reflection layer 260 may be formed by CVD, PVD, ALD, sputtering, or the like. In further embodiments, the anti-reflection layer 260 may be planarized (e.g., via CMP) subsequent to formation.

Also shown in FIGS. 10A-10C, a plurality of color filters 262 (e.g., a red color filer, a blue color filter, a green color filer, etc.) are formed on the anti-reflection layer 260. In some embodiments, center points of the plurality of color filters 262 are substantially aligned in a vertical direction with center points of the photodetector collector regions 108, respectively. In further embodiments, the plurality of color filters 262 may be formed by forming various color filter layers and patterning the color filter layers. The color filter layers are formed of material that allows for the transmission of radiation (e.g., light) having a specific wavelength range, while blocking light of wavelengths outside of the specified range. Further, in some embodiments, the color filter layers may be planarized (e.g., via CMP) subsequent to formation.

A plurality of micro-lenses 264 are formed over the plurality of color filters 262. In some embodiments, center points of the micro-lenses 264 are substantially aligned in a vertical direction with center points of the color filters 262, respectively. In further embodiments, the micro-lenses 264 may be formed by depositing a micro-lens material on the color filters 262 (e.g., by a spin-on method or a deposition process). A micro-lens template (not shown) having a curved upper surface is patterned above the micro-lens material. In some embodiments, the micro-lens template may comprise a photoresist material exposed using a distributing exposing light dose (e.g., for a negative photoresist more light is exposed at a bottom of the curvature and less light is exposed at a top of the curvature), developed and baked to form a rounding shape. The micro-lenses 264 are then formed by selectively etching the micro-lens material according to the micro-lens template.

As illustrated in FIG. 11, a flowchart 1100 of some embodiments of a method for forming the integrated chip (IC) of FIGS. 2A-2C is provided. While the flowchart 1100 of FIG. 11 is illustrated and described herein as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events is not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. Further, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein, and one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases.

At 1102, a pixel device region isolation structure is formed in a semiconductor substrate. FIGS. 4A-4C illustrate various views of some embodiments corresponding to act 1102.

At 1104, a pixel sensor well region is formed in the semiconductor substrate. FIGS. 5A-5C illustrate various views of some embodiments corresponding to act 1104.

At 1106, a first, a second, a third, and a fourth photodetector are formed in the pixel sensor well region, where a first substantially straight line axis intersects a center point of the first photodetector and a center point of the second photodetector, and where a second substantially straight line axis that is substantially parallel to the first substantially straight line axis intersects a center point of the third photodetector and a center point of the fourth photodetector. FIGS. 5A-5C illustrate various views of some embodiments corresponding to act 1106.

At 1108, transfer transistor gate electrodes, transfer transistor gate dielectrics, transfer transistor sidewall spacers, pixel device gate electrodes, pixel device gate dielectrics, and pixel device sidewall spacers are formed over a front-side of the semiconductor substrate. FIGS. 6A-6C illustrate various views of some embodiments corresponding to act 1108.

At 1110, source/drain regions are formed in the pixel sensor well region on opposite sides of the pixel device gate electrodes. FIGS. 7A-7C illustrate various views of some embodiments corresponding to act 1110.

At 1112, a floating diffusion node is formed in the pixel sensor well region between the first photodetector, the second photodetector, the third photodetector, and the fourth photodetector. FIGS. 7A-7C illustrate various views of some embodiments corresponding to act 1112.

At 1114, a pick-up well contact region is formed spaced from the floating diffusion node in the pixel sensor well region, where a third substantially straight line axis that is substantially perpendicular to the first substantially straight line axis intersects a center point of the pick-up well contact region and a center point of the floating diffusion node. FIGS. 7A-7C illustrate various views of some embodiments corresponding to act 1114.

At 1116, an interconnect structure is formed on the front-side of the semiconductor substrate. FIGS. 8A-8C illustrate various views of some embodiments corresponding to act 1116.

At 1118, back-side isolation structures are formed in the semiconductor substrate, where the back-side isolation structures extend into the semiconductor substrate from a back-side of the semiconductor substrate. FIGS. 9A-9C illustrate various views of some embodiments corresponding to act 1118.

At 1120, an anti-reflection layer is formed on the interconnect structure and the back-side isolation structures, a plurality of color filters are formed on the anti-reflection layer, and a plurality of micro-lens are formed on the color filters. FIGS. 10A-10C illustrate various views of some embodiments corresponding to act 1120.

In some embodiments, the present application provides a pixel sensor. The pixel sensor includes a first photodetector disposed in a semiconductor substrate. A second photodetector is disposed in the semiconductor substrate, where a first substantially straight line axis intersects a center point of the first photodetector and a center point of the second photodetector. A floating diffusion node is disposed in the semiconductor substrate at a point that is a substantially equal distance from the first photodetector and the second photodetector. A pick-up well contact region is disposed in the semiconductor substrate, where a second substantially straight line axis that is substantially perpendicular to the first substantially straight line axis intersects a center point of the floating diffusion node and a center point of the pick-up well contact region.

In other embodiments, the present application provides an image sensor. The image sensor includes a first floating diffusion node disposed in a first pixel sensor well region that is disposed in the semiconductor substrate. A plurality of first photodetectors are disposed in the first pixel sensor well region, where the plurality of first photodetectors includes a first photodetector and a second photodetector separated from the first floating diffusion node by substantially equal distances. A second floating diffusion node is disposed in a second pixel sensor well region that is disposed in the semiconductor substrate. A plurality of second photodetectors is disposed in the second pixel sensor well region, where the plurality of second photodetectors includes a third photodetector and a fourth photodetector separated from the second floating diffusion node by substantially equal distances. A first pick-up well contact region is disposed in the semiconductor substrate between the plurality of first photodetectors and the plurality of second photodetectors, where a first line intersects the first floating diffusion node, the second floating diffusion node, and the first pick-up well contact region.

In yet other embodiments, the present application provides a method for forming a pixel sensor. The method includes forming a first doped well region having a first doping type in a semiconductor substrate. A first photodetector collector region having a second doping type different than the first doping type is formed in the semiconductor substrate. A second photodetector collector region having the second doping type is formed in the semiconductor substrate and spaced from the first photodetector collector region, where a first line intersects the first photodetector collector region and the second photodetector collector region. A floating diffusion node is formed in the semiconductor substrate between the first photodetector collector region and the second photodetector collector region. A pick-up well contact region having the first doping type is formed in the first doped well region, where the pick-up well contact region has a higher concentration of the first doping type than the first doped well region, and where a second line that is substantially perpendicular to the first line intersects the floating diffusion node and the pick-up well contact region.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A pixel sensor, comprising: a first photodetector disposed in a semiconductor substrate; a second photodetector disposed in the semiconductor substrate, wherein a first substantially straight line axis intersects a center point of the first photodetector and a center point of the second photodetector; a floating diffusion node disposed in the semiconductor substrate at a point that is a substantially equal distance from the first photodetector and the second photodetector; a pick-up well contact region disposed in the semiconductor substrate, wherein a second substantially straight line axis that is substantially perpendicular to the first substantially straight line axis intersects a center point of the floating diffusion node and a center point of the pick-up well contact region; and a pixel device region disposed on a first side of the first substantially straight line axis, wherein the pixel device region comprises a source follower transistor, wherein the source follower transistor comprises a pair of source/drain regions, and wherein a third substantially straight line axis that is substantially parallel with the first substantially straight line axis intersect the pick-up well contact region and the source/drain regions.
 2. The pixel sensor of claim 1, further comprising: a first transfer transistor at least partially disposed over the first photodetector, wherein the first transfer transistor is disposed between the center point of the first photodetector and the floating diffusion node; and a second transfer transistor at least partially disposed over the second photodetector, wherein the second transfer transistor is disposed between the center point of the second photodetector and the floating diffusion node.
 3. The pixel sensor of claim 1, wherein: the floating diffusion node is disposed on a second side of the first substantially straight line axis opposite the first side; and the pick-up well contact region is disposed on the first side of the first substantially straight line axis.
 4. The pixel sensor of claim 1, wherein: the first photodetector comprises a first collector region; the second photodetector comprises a second collector region; and the second substantially straight line axis extends laterally between the first collector region and the second collector region.
 5. The pixel sensor of claim 1, wherein the second substantially straight line axis intersects the first substantially straight line axis at a mid-point between the center point of the first photodetector and the center point of the second photodetector.
 6. The pixel sensor of claim 1, further comprising: a third photodetector disposed in the semiconductor substrate; and a fourth photodetector disposed in the semiconductor substrate, wherein a fourth substantially straight line axis that is substantially parallel with the first substantially straight line axis intersects a center point of the third photodetector and a center point of the fourth photodetector, and wherein the floating diffusion node is disposed between the first substantially straight line axis and the third fourth substantially straight line axis.
 7. The pixel sensor of claim 6, wherein the center point of the floating diffusion node is spaced about a same distance from the first substantially straight line axis as the fourth substantially straight line axis.
 8. The pixel sensor of claim 7, wherein the center point of the first photodetector, the center point of the second photodetector, the center point of the third photodetector, and the center point of the fourth photodetector are spaced about evenly from the center point of the floating diffusion node.
 9. The pixel sensor of claim 8, wherein the third substantially straight line axis intersect the center point of the pick-up well contact region and center points of the source/drain regions.
 10. The pixel sensor of claim 9, further comprising: a pixel device region isolation structure disposed in the semiconductor substrate, wherein the pixel device region isolation structure is ring-shaped, and wherein outer sidewalls of the pixel device region isolation structure define outer sides of the pixel device region; a reset transistor disposed in the pixel device region, wherein one of the source/drain regions is a first common source/drain region between the reset transistor and the source follower transistor; and a select transistor disposed in the pixel device region, wherein another one of the source/drain regions is a second common source/drain region between the select transistor and the source follower transistor.
 11. The pixel sensor of claim 10, wherein the pick-up well contact region is disposed outside the pixel device region.
 12. The pixel sensor of claim 11, further comprising: a doped well region comprising a first doping type disposed in the semiconductor substrate and surrounding the first photodetector, the second photodetector, the third photodetector, and the fourth photodetector, wherein the pick-up well contact region is disposed in the doped well region and comprises a higher concentration of the first doping type than the doped well region.
 13. An image sensor, comprising: a first floating diffusion node disposed in a first pixel sensor well region that is disposed in a semiconductor substrate; a first plurality of photodetectors disposed in the first pixel sensor well region, wherein the first plurality of photodetectors comprises a first photodetector and a second photodetector separated from the first floating diffusion node by substantially equal distances; a second floating diffusion node disposed in a second pixel sensor well region that is disposed in the semiconductor substrate; a second plurality of photodetectors disposed in the second pixel sensor well region, wherein the second plurality of photodetectors comprises a third photodetector and a fourth photodetector separated from the second floating diffusion node by substantially equal distances; a first pick-up well contact region disposed in the semiconductor substrate between the first plurality of photodetectors and the second plurality of photodetectors, wherein a first line intersects the first floating diffusion node, the second floating diffusion node, and the first pick-up well contact region; and a first pixel device region comprising a first source follower transistor disposed in the semiconductor substrate between the first plurality of photodetectors and the second plurality of photodetectors, wherein the first source follower transistor comprises a pair of first source/drain regions, and wherein a second line that is substantially perpendicular to the first line intersects the first pick-up well contact region and one of the first source/drain regions.
 14. The image sensor of claim 13, wherein: center points of the first plurality of photodetectors are spaced about evenly from a center point of the first floating diffusion node; and center points of the second plurality of photodetectors are spaced about evenly from a center point of the second floating diffusion node.
 15. The image sensor of claim 13, wherein the second line intersects a center point of the first pick-up well contact region and a center point of one of the first source/drain regions.
 16. The image sensor of claim 15, further comprising: a second pick-up well contact region disposed in the semiconductor substrate on a side of the second plurality of photodetectors opposite the first pick-up well contact region, wherein the first line intersects a center point of the second pick-up well contact region; and a second pixel device region comprising a second source follower transistor disposed in the semiconductor substrate on a same side of the second plurality of photodetectors as the second pick-up well contact region, wherein the second source follower transistor comprises a pair of second source/drain regions, and wherein a third line that is substantially parallel with the second line intersects the center point of the second pick-up well contact region and a center point of one of the second source/drain regions.
 17. The image sensor of claim 16, wherein: the first floating diffusion node and the second floating diffusion node are spaced about a same distance from the first pick-up well contact region; and the second pick-up well contact region is spaced from the second floating diffusion node by about the same distance the first floating diffusion node is spaced from the first pick-up well contact region.
 18. The image sensor of claim 15, wherein: a fourth line that is substantially parallel with the first line intersects a center point of the first photodetector and a center point of the third photodetector; and a fifth line that is substantially parallel with the fourth line intersects the second photodetector and the fourth photodetector.
 19. The image sensor of claim 18, further comprising: a third pixel sensor well region disposed in the semiconductor substrate; a third floating diffusion node disposed in the third pixel sensor well region; a fifth photodetector and a sixth photodetector disposed in the third pixel sensor well region and separated from the third floating diffusion node by substantially equal distances, wherein a sixth line that is substantially perpendicular to the fourth line intersects a center point of the second photodetector, a center point of the fifth photodetector, and a center point of the sixth photodetector; and a pixel device region isolation structure disposed in the semiconductor substrate, wherein the pixel device region isolation structure defines outer sides of the first pixel device region, wherein the fifth line intersects the pixel device region isolation structure at a first point, and wherein a seventh line that is substantially parallel with the fifth line intersects the center point of the fifth photodetector and intersects the pixel device region isolation structure at a second point different than the first point.
 20. A method for forming a pixel sensor, the method comprising: forming a first doped well region having a first doping type in a semiconductor substrate; forming a first photodetector collector region having a second doping type different than the first doping type in the semiconductor substrate; forming a second photodetector collector region having the second doping type in the semiconductor substrate and spaced from the first photodetector collector region, wherein a first line intersects the first photodetector collector region and the second photodetector collector region; forming a floating diffusion node in the semiconductor substrate between the first photodetector collector region and the second photodetector collector region; and forming a pick-up well contact region having the first doping type in the first doped well region, wherein the pick-up well contact region has a higher concentration of the first doping type than the first doped well region, and wherein a second line that is substantially perpendicular to the first line intersects the floating diffusion node and the pick-up well contact region. 